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Reading ECGs

Dr Sherwan R Shal2007

Exclusive

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YOU should have the following information:

• Patients IDs e.g. name, • Date (in years, months, days, hours and

minutes).• Place where ECG was taken.• ALL written or printed on the ECG paper

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You should be able to..Differentiate normal from abnormal ECG.And at this level:1. Heart rate.2. Rhythm.3. Time duration.4. Voltage amplitude.5. Heart axis, deviations to right or left.6. Overall wave forms and configuration.

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• ECG is recorded on a paper which is divided by horizontal and vertical lines forming squares.

• A large square is divide into 25 small squares.• One large square is (5 X 5) square mm; i.e.

5mm length and 5mm width.

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• Each large square is divide into 25 small squares. 5 raws and 5 columns.

• Each small square is 1X1 square mm; i.e. 1mm in length and 1mm width.

1 2 3 4 52345

1 mm

5 mm

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• The normal speed of the ECG paper is 25mm/second. • This is equal to 25 small squares per second.• This also means 5 large squares per second.

1 2 3 4 5

2

3

4

5

1 2 3 4 5

2

3

4

5

1 2 3 4 5

2

3

4

5

1 2 3 4 5

2

3

4

5

1 2 3 4 5

2

3

4

5

25 small squares

21 4 53

One large square

Speed = 25 mm/second

5 large squares/second

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• Horizontal line represents time.• So, one small square equals to 1/25 second or equals to 0.04

second.• And, one large square equals to 1/5 second or 0.2 second.

5 4 3 2 1

5 large squares= one second

One large square= 0.2 second

25 small squares= one second

one small square= 0.04 second

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• Vertical line represents voltage.• Traditionally, every 1o small squares (or 2 large squares) up or down is 1mV.• So, one small square is 1/10 or 0.1 mV.• And, one large square is ½ mV or )0.5 mV.

Two large Squares

1 mV

One large square0.5 mV

One small square0.1 mV

1

2

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Measurements1. Measurements

Heart Rate: 60 - 100 bpm PR Interval: 0.12 - 0.20 sec (= 3 to 5 small sq.)QRS Duration: 0.06 - 0.10 sec (= 1.5 to 2.5 small sq.) QT Interval (QTc < 0.40 sec) (= ≤ 10 small sq.)QT < 0.42 @ 60 bpm

Corrected QT interval = QT interval /√ (RR) interval

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Measurements2. Rhythm: Normal sinus rhythm:

The P waves in leads I and II must be upright (positive) if the rhythm is coming from the sinus node.

3. Conduction:Normal Sino-atrial (SA), Atrio-ventricular (AV), and Intraventricular

(IV) conductionBoth the PR interval and QRS duration should be within the limits

specified above. P Wave P duration < 0.12 sec P amplitude < 2.5 mmQRS Complex QRS duration < 0.10 sec

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Normal Voltages in the Electrocardiogram

The voltage of the QRS complex usually is 1.0 to 1.5 millivolt from the top of the R wave to the bottom of the S wave;

The voltage of the P wave is between 0.1 and 0.3 millivolt;

The voltage of T wave is between 0.2 and 0.3 millivolt.

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P-Q or P-R Interval The time between the beginning of the P wave and the

beginning of the QRS complex is the interval between the beginning of electrical excitation of the atria and the beginning of excitation of the ventricles.

This period is called the P-Q interval. The normal P-Q interval is about 0.16 second. (Often this

interval is called the P-R interval because the Q wave is likely to be absent.)

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Heart Rate• Heart rate is measured in beats/minute.• ECG paper speed is in mm/second, so we

should change it to mm/minutes.• 25 mm/second equals to 60X25 mm/second• = 1500 mm/min. (1500 small sq/min.)• = 1500/5 =300 large sq. /min.

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Heart Rate• One heart beat is one cardiac cycle.• One cardiac cycle starts from one wave e.g. R

wave , to the next R wave (or from p to next p)• Count the number of small sq. between two

successive R waves,• OR the number of large sq. between two RR.

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Heart Rate

= 1500 / No. of small sq. bet. 2 RR waves

= 300/ No. of large sq. bet. 2 RR waves .

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Applications

P

Q

QRS T

RR interval

Time (seconds)Volta

ge (m

V)

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Applications

91 2 3 4 5 6 7 8

P

Q

QRS T

Heart rateP durationP VoltageQRS durationQT durationT timeT amplitude

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Regular RhythmRegular if the distance between two successive R waves R regular and all other wave are found and sinus

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Irregular RhythmIrregular if the distance between two successive R waves R is irregular

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Physiological Causes of axis deviation

• When the diaphragm ascends up with expiration, the heart becomes more horizontal (i.e. deviates to the left)

• Inspiration, on the other hand, makes the diaphragm to descends down, and the heart will be hanged or vertical (i.e. right axis)

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Physiological Causes of axis deviation

• Diaphragm moves down with inspiration, standing (because abdominal contents descends) this happen also with tall persons.

• Diaphragm moves up with expiration, lying down, or in fatty person and any cause of increased intraabdominal mass (like pregnancy)

AXIS DEVIATION

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Horizontal HeartLAD

Normal

Vertical Heart

RAD

Heart

Diaphragm

The axis of the heartNormal cardiac axis is about 58o

It is close to lead IIIt might shift to the left or to the right

Left

Right

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Left AxisAxis is to the left of hexagonal reference system.Angle is near zero and less

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Left AxisAxis is to the left of hexagonal reference system.Angle is near zero and less

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Right AxisAxis is to the right of hexagonal reference system.Angle is near 90 and more

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Right AxisAxis is to the right of hexagonal reference system.Angle is near 90 and more

Left and Right axis

IIII

IIII

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RADLAD

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Left axis deviation Right axis deviation

I

II

III

I

II

III

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Normal

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Test Your Knowledge

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Test Your Knowledge

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Test Your Knowledge